![]() ![]() Where as human vision appears to operate on an opponent process model, some animals with more diverse varieties of color receptors have been show to operate on different methods of color perception. Ironically the mantis shrimp, the animal that could have the broadest, most detailed perception of color with 12 different color receptors, may not see in such the vivid arrangement that was previously thought. Behavioral methods have been designed which are used to better understand how many different colors animals are able to differentiate between (how many different colors are perceived) compared to how many different types of receptors they have (see Gregg, Jamison, Wilkie & Radinsky, 1924, for example of color differentiation between dogs, cats and raccoons). Humans and animals perceive color by way of an opponent processing model of color vision where a small amount of primary color receptors mix their signals to create the perceptions of a variety of other colors (Herring, 1924). Dogs commonly thought to see in black and white actually do see in color, however their perception is limited to a more narrow arrangement of colors including black, yellow, gray and blue. Humans have three different types of color receptors (cones) resulting in a trichromatic organization of color, whereas most birds have four different types of cones resulting in a tetrachromatic experience including gray, blue, green and red. (An easy way to remember this is the mnemonic ROYGBIV: red, orange, yellow, green, blue, indigo, violet.) The amplitude of light waves is associated with our experience of brightness or intensity of color, with larger amplitudes appearing brighter. Animals that are able to see visible light have different ranges of color perception. Within the visible spectrum, our experience of red is associated with longer wavelengths, greens are intermediate, and blues and violets are shorter in wavelength. In humans, light wavelength is associated with perception of color (figure above). Light that is visible to humans makes up only a small portion of the electromagnetic spectrum. For instance, honeybees can see light in the ultraviolet range (Wakakuwa, Stavenga, & Arikawa, 2007), and some snakes can detect infrared radiation in addition to more traditional visual light cues (Chen, Deng, Brauth, Ding, & Tang, 2012 Hartline, Kass, & Loop, 1978). Other species can detect other portions of the electromagnetic spectrum. The visible spectrum in humans is associated with wavelengths that range from 380 to 740 nm-a very small distance, since a nanometer (nm) is one billionth of a meter. These waves are everywhere around us at all times but for some waveforms we need to use sophisticated tools in order to translate this information into visible light waves we are able to see. As the figure below shows, the electromagnetic spectrum encompasses all of the electromagnetic radiation that occurs in our environment and includes gamma rays, x-rays, ultraviolet light, visible light, infrared light, microwaves, and radio waves. The visible spectrum is the portion of the larger electromagnetic spectrum that we can see. Moving from top to bottom, the wavelengths decrease and frequencies increase. At the top of the figure, the red wave has a long wavelength/short frequency. This figure illustrates waves of differing wavelengths/frequencies. Longer wavelengths will have lower frequencies, and shorter wavelengths will have higher frequencies (figure below). Frequency refers to the number of waves that pass a given point in a given time period and is often expressed in terms of hertz (Hz), or cycles per second. Wavelength is directly related to the frequency of a given wave form. The wavelength is measured from peak to peak. The amplitude or height of a wave is measured from the peak to the trough. Wavelength refers to the length of a wave from one peak to the next. The amplitude of a wave is the height of a wave as measured from the highest point on the wave (peak or crest) to the lowest point on the wave (trough). Two physical characteristics of a wave are amplitude and wavelength (figure below). In this section, we describe the physical properties of the waves as well as the perceptual experiences associated with them. Waveforms of different types surround us at all times, however we only have receptors which are sensitive to specific types of wavelengths. Although the two stimuli are very different in terms of composition, wave forms share similar characteristics that are especially important to our visual and auditory perceptions. Visual and auditory stimuli both occur in the form of waves. Show how physical properties of sound waves are associated with perceptual experience.Show how physical properties of light waves are associated with perceptual experience.Describe important physical features of wave forms.By the end of this section, you will be able to: ![]()
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